I suppose it would depend what kind of cup was holding the acid as to whether it would indeed burn a hole through, and if it would, the type of cup would determine how long it would take for it to happen, so the woman could stand there for that amount of time before the cup actually began to be eaten away. Didn't like this one at all.

Of course acid wouldn't go through the cup... it wasn't a paper cup. In fact it wasn't specified. Could have been a tin or glass cup. The type of acid wasn't specified either... could have been a very mild acid as was suggested in several other comments.

Not my favorite teaser... sorry. It just didn't have any challenge at all to it.